Primary Lithium Battery: 9V 1200mAh (10.8Wh, 50mA rate) Compatible with Energizer L522-9V / Ultralife - UL Listed / UN 38.3 Passed (NDGR)
9V Batteries Suck - And why you shouldn't use them. - Bald Engineer
HQRP USB 9V Lithium-Ion Rechargeable Battery, High Capacity 500mAh 9-Volt, 1.5 H Fast Charge, 800 Cycle with Micro USB Cable, Radio Square 6LR61 7.2H5 6KR61 6HR61 PP3 MN1604 - Walmart.com